Concentrators for solar energy have been in use for many years. These devices are used to focus the sun's energy into a small area to raise the power level being concentrated on a photovoltaic converter to generate electrical power directly, or on a fluid line to heat water to make steam to drive a turbine to generate electrical power.
One difficulty with these concentrators has been that they are generally large and bulky and are not suitable for residential applications or other locations where the aesthetics of the installation are of importance. Additionally, they are very susceptible to environmental damage due to wind and other elements.
Thin film solar panels have been used extensively in recent years for installations on buildings and homes. These panels may be articulated in one or two dimensions or may be fixed. A fixed installation is the least expensive implementation but is also the least efficient because the plane of the panel is rarely normal (90°) to the solar axis. A single point of articulation that allows a panel to track the angle of the sun during the day improves on this approach but there will still be an angle. A second, orthogonal point of articulation will allow a panel to track the sun and maintain the panel so that the solar axis is normal to the plane of the panel. Such systems are inherently bulky and in general are considered more suitable for surface installations than for roof top installations.
An additional problem with roof top installations of any type is the problem of shading. Shading often occurs by environmental features such as trees or tall buildings nearby. Little or nothing can be done about these other than using good planning and commonly available software tools. The difficulty that shading poses is that it can also affect the output of portions of a solar installation that are not placed in the shading because of electrical interaction between the shaded areas and the unshaded areas of the solar installation. This phenomenon is understood and is well reported in the literature. “Shading Effects on Output Power of Grid Connect Photovoltaic Generator Systems,” Hanitsch et al, Rev. Energ. Ren.: Power Engineering (2001) 93-99, provides enlightening information on the matter.
Another cause of shading relates to installation factors. Individual solar concentrator assemblies may shade adjacent solar concentrator assemblies at times of the day, with sunrise and/or sunset being the most frequent times. Solutions to these problems depend on the type of solar system involved. A solution for concentrating solar energy systems is particularly difficult. A consideration of solutions is presented in the present application.
FIG. 1 presents a prior art solution for the need to keep the optical axes of a plurality of trough mirrors aligned while moving the trough mirrors to maintain alignment with the sun. Articulating solar concentrator system 10 comprises trough mirrors 25, solar energy collecting tubes 40, support 30, energy transmitting tube 35, trough mirror linking rod 20 and linking rod actuator 15. Trough mirrors 25 are arrayed parallel to one another with solar energy collecting tubes 40 at the focal point of the trough mirrors 25. Solar energy collecting tubes 40 are each physically connected to one of the trough mirrors 25 and are supported by mounting assemblies 30 such that all energy collecting tubes 40 lie in the same plane. Energy transmitting tube 35 connects to each collecting tube 40 by a sealed fitting or the like as is well known in the art. Energy transmitting tube 35 is supported by energy collecting tubes 40. Energy transmitting tube may be connected to a suitable energy harvesting system (not shown) such as a turbine or a hot water heater as is well known in the art. Linking rod 20 is connecting to each of the trough mirrors 25 by an articulating component (not shown). When linking rod 20 is moved by linking rod actuator 15 all trough mirror respond by rotating in the same direction. In this implementation the movement of trough mirrors 25 enables solar concentrator system 10 to track the sun during the course of a day.
Wire cables have long been used as a way of transferring mechanical energy from one location to another. Wire cables are used in diverse applications such as moving the control surfaces of aircraft and moving the print head of dot matrix printers.
One example is the Texas Instruments TI810BSC, designed by the inventor of the present disclosure, which was used for an extended period of time in the airline industry to print tickets and baggage tags. The printer uses a driver pulley to move the print head back and forth across the paper or other material to be printed by moving a wire cable. The wire cable loops over an idler pulley and is routed back to the driver pulley. A tensioner pulley is typically added in the return path of the wire cable. The interior of a dot matrix printer is a hostile environment because in decades of service a significant amount of paper lint and dust will accumulate there. The wire cable drive arrangements work well in that environment and also return the print head to a precise position.
Many of these wire cables are pre-stretched to minimize the development of additional slack in the wire cable during extended operation. The slack occurs as a natural consequence of the catenary effects of gravity on any cable suspended from two ends. The slack follows the shape of the hyperbolic cosine function. The slack becomes problematic as the driver pulley reverses its direction of motion. Too much slack can lead to an unacceptable level of play.
The present disclosure seeks to overcome the foregoing difficulties associated with rooftop installations while maintaining the ability to track the sun in two axes through the use of pulleys driven by wire cables.
The subject matter of the present disclosure is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.